Adjusting compound-wound generator.



'No. 7l3,523. Patented Nov. II, I902. C. P. STEINNETZ.

ADJUSTING COMPOUND WOUND GENERATORS.

(Application filed Aug. 24, 1898.) (No Model.) 2 Sheets-Sheet l.

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No. 7l3,523. Patentod Nov. ll, I902.

C. P. STEINIETZ.

ADJUSTING COIPOUND WOUND GENERATORS.

(Applimflon and Aug. u, use.)

(No lodol.) 2 Sheets-Shoot 2.

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UNITED STATES PATENT OFFICE.

CHARLES P. STEINMETZ, OF SCHENECTADY, NEIV YORK, ASSIGNOR TO GEN- ERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ADJUSTING COMPOUND-WOUND GENERATOR.

SPECIFICATION forming part of Letters Patent No. 713,523, dated November 11, 1902.

Application filed Angnst24,1898. Serial No. 689.392. (No model.) I

To all whom it may concern.-

Be it known that I, CHARLES P. STEINMETZ, a citizen of the United States, residing at Schenectady, in the county of Schenectady and State of New York, have invented certain new and useful Improvements in Adjusting Com pound-Wound Generators, (Case No. 839,) of which the following is a specification.

The magnetic characteristic or saturation.

curve of a dynamo-electric machine is always to a certain extent curved, for the reason that the magnetization does not increase at the same rate as the increase of magnetizing or exciting current. Since the external characteristic or load curve of a dynamo-electric machine is always to a certain extent dependent for its shape upon the magnetic characteristic or saturation curve of the magnetic circuit of the machine, it follows that the load curve or external characteristic is correspondingly curved. Thus when compounding a self-exciting direct-current generator for constant potential the voltage at half load will be higher than at no load and at full load. In a similar manner when overcompounding such a machine by the use of a series field the ampere-turns of which are proportional to the load the voltage does not rise proportionally to the increase in load, but rises at a decreasing rate corresponding to the decreasing rate of increase of flux in the magnetic circuit. The voltage thus rises more from no load to half load than from half load to full load. It is the purpose of my invention to compensate for this variation in voltage due to the variation in permeability of the magnetic circuit, and I accomplish the result by varying the field magnetomotive force or forces at a rate greater than the rate of variation of load.

I believe myself to be the first to accomplish the result described, and although the various means devised by me and disclosed in this application operate Without the aid of moving parts I, nevertheless, deem my invention a generic one and broad enough to include the use of automaticallyactuated moving parts for the purpose described.

I have described in the specification and illustrated in the accompanying drawings several modes of carrying out my invention; but I do not wish to be understood as limitin g myself specifically to any one of the means show modified forms of the same.

In Fig. 1 I have shown my invention as applied to a self-exciting direct-current dynamoelectric machine having series and shunt coils. In order to straighten'the external characteristic of the machine, it is necessary to increase the ampere-turns of the series winding at a rate greater than the increase of load on the machine. This result I accomplish in the present instance by shunting the series coil with a resistance havinga temperature coeflicient greater than that of the series coilin other words, by a device the resistance of which increases with increase of current faster than the resistance of the series coil increases under similar conditions. If, as is usually the case, the series coil is formed of copper, I may employ iron as the material of which to form the shunt about the series coil, though it is obvious that the use of any other material is equally within the scope of my invention.

In the drawings, 1 represents the armature of the direct-current dynamo-electric machine. Connected in series therewith in the usual manner is the series exciting-coil 2. Shunted around the series coil is the variableresistance coil 3 of the character described that is to say, having a temperature coefficient higher than that of the series coil. This resistance is arranged to be varied simply for the purpose of initial adjustment, and it is not in general intended to be altered during the normal operation of the machine, although, ifdesired, such use is not prohibited. For this purpose a switch-arm 9, with cooperating contacts, may be employed. In shunt with the brushes in the usual manner is the shunt-exciting coil 4, having in series therewith the usual variable regulatirig-resistance 5.

In the operation of the form of my invention described it will be obvious that as the current supplied either to or from the machine increases the current through the series coil and the resistance in shunt thereto will divide in certain proportions. As the current through the machine increases the branch currents through the series coil 2 and its shunted resistance 3 increase. Owingto the fact, however, that the resistance of the sh unt 3 increases with increase of current faster than the resistance of series coil 2, it follows that a greater proportion of current will pass through the series coil at higher values of load than at lower. By suitably adjusting the resistance of the shunt 3 a value may be found such that the current passing through the series coil 2 increases faster than the load by an amount just sufficient to compensate for the drop in voltage due to the decreasing permeability of the magnetic circuit. The loadcurve thus becomes a straight line.

In Fig. 2 is shown a somewhat-dilferent arrangement foraccomplishing the same purpose. As before, 1 denotes the armature of a dynamo electric machine, around the brushes of which is connected the shunt-winding 4. In series with the armature is a series exciting-coil 2. In order to increase the ampere-turns of the series field faster than the increase of load, I place in series with said coil a counter electromotive-force device 6,

the counter electromotive force of which increases at a rate less than proportional to the current passing through said device. For this purpose I preferably employ polarizationcells or a suitable number of elements of a storage battery. The electromotive force consu med in passing current through a device of this character is composed of two quantities. One is the counter electromotive force proper of the device and is sensibly constant through considerable variations of current. The other is the electromotive force consumed by the resistance of the device, and this is proportional to the current. It consequently follows that the electromotive force consumed in the counter electromotive-force device is less than proportional to the current passing through the same.

Referring again to Fig. 2, it will be noted that the series coil 2 and the counter electromotive-force device 6 are shunted by the resistance 7. For the present purpose this resistance may preferably have as low a temperature coefifilcient as possible, so as to remain practically constant with changes of current. The mode of operation will be apparent from what has been said. The current passing either to or from the machine willdivide, part going through the series coil and the counter electromotive-force device, the other part going through the shunt about the same. Since the resistance of the shunt 7 is nearly constant, the drop of potential across the same will be almost exactly proportional to the current passing. With respect to the series coil, however, the state of afiairs is different. The electromotive'force lost in passing the current through the same varies with the current, being less in proportion when the current is large than when it is small.

It will'be seen, therefore, that the ratio in which current will divide between the series coil and the shunt 7 will vary with the load. A greater proportion of the current will pass through the series coil at heavy 'loads than at light ones, and'thus compensate for the drop in potential due to the curving magnetic characteristic of the machine.

In Fig. 3 is shown another modification in the embodiment of my invention. In this case, as in the others, 1 represents the armature of a dynamo-electro machine, shunted around the brushes of which is the shunt-exciting coil 4. The series magnetizing-coil is shown at 2,and this coil has in series therewith a resistance 8, having a negative temperature coefficientthat is, a resistance which decreasesin value with increase in temperature or what amounts to the samething with increase of current passing through it. The resistance 7 is shunted around the series coil 2 and the resistance 8. The shunt-resistance 7 should have as lowa temperature coefficient as possible, so as to vary but little in resistance with the varying value of current passing through it. In the operation of the machine as thus arranged current will divide between the two branch circuits described in inverse proportion to their respective resistances. Owing to the fact that the resistance 8 decreases with increase of current, while the resistance of the shunt 7 remains sensibly constant, it follows that a greater proportion of current will pass through the series fieldcoil at heavy loads than at light loads, andthus obtain the same result accomplished by the two modifications of myinvention' already described. Ipreferably employ carbon as the material from which to construct the resistance S. It will. be evident that instead of employing a resistance 8, having a negative temperature coefficient, it will be suflicient if I employ materials having temperature coeflicients such that the ratio between the resistance 7 and the combined resistance of the series coil and its resistance 8 becomes greater as the load increases. I findit convenient to construct the shunt-resistance 7 of German silver.

Although in connection with Figs. 2 and 3 of the drawings I have described certain modifications of my invention in which the regulating shunt-resistance 7 has a low tempera-' ture coeflicient, it is evident that the same result may be produced, but in a greater degree, by making the regulating-resistance 7 of material having a high temperature 00- efficient, since the conditions requisite tocarrying out my invention are efiected so long as the current through the series coil is caused to vary at a rate greater than the variation of load on the machine.

My invention is to be sharply distinguished from the commonly-used structure, in which a German-silver shunt is placed about the series winding of a compound machine in order to initially adjust its magnetizing power. In this case the mode of action is radically different from that of my invention, since a smaller,instead of a larger, proportion of the total current will pass through the series coil at heavy loads than at light loads, thus tending to destroy rather than help the regulation.

Instead of relying upon any particular one of the instrumentalities described I may, if deemed expedient, employ them in conjunction, as illustrated in Fig. 4. In this figure 1 designates, as before, the armature of a dynamo electric machine having the shunt field-winding 4 and series compounding-coil 2. A resistance 8 of negative temperature coefficient and polarization-cells 6 areincluded in series with each other and with the series coil 2. A resistance of iron or other material of high temperature coefficient forms a derived circuit in parallel with the circuit, including the series coil 2, resistance 8, and polarization-cells 6. From what has already been said in connection with the other figures of the drawings it will readily be seen that as the load on the machine increases the current through the series compounding-coil will also increase, but at a rate greater than the rate of increase of load.

Still another application of my invention is found in the case where a shunt-wound generator is used as a constant-current machine to supply translating devices in series, in which case the machine is worked within the range included by the bend in its characteristic curve. With machines specially designed to be operated in this manner the voltage may be varied through a considerable range without varying the current to any great extent. So long as saturation is not reached or closely approached the voltage at the terminals of the machine is proportional to the excitation, and the excitation is approximately proportional to the resistance of the work-circuit. As the load increases, however, the magnetization of the field approaches saturation, so that the voltage of the machine does not increase in proportion to the current through the shunt-field, and the current in the work-circuit therefore decreases instead of remaining constant, as desired. To compensate for the eifect of saturation in the case described, I insert in the shunt-field a resistance having a high negative temperature coefficient, the eifect of which is to cause an increase of current through the shunt-winding more than proportional to the increase of electromotive force at the terminals of the machine. By a suitable proportioning of parts the effect of changing permeability of the magnetic circuit of the machine may thus be compensated for.

Fig. 5 is a diagrammatic illustration of the form of myinvention just described, in which 1 represents the armature of a shunt-wound generator having the field-winding 12. In

series with said winding is a resistance 10, having a negative temperature coefficient. This resistance is preferably formed of carwhen I speak of a load on a dynamo-electric machine the term is intended to include both the electrical load when the machine is used as a generator and the mechanical load when the machine is used as a motor.

What I claim as new, and desire to secure by Letters Patent of the United States, is

1. The method of regulating a dynamoelectric machine which consists in automatically compensating for the variation in voltage due to variation in permeability of the magnetic circuit.

2. The method of regulating a dynamoelectric machine which consists in automatically compensating for the efifect due to variation in permeability of the magnetic circuit.

3. The method of regulating a dynamoelectric machine, which consists in diverting current from a field-coil of the machine in such proportions that the ratio between the current diverted and that passing in the coil is less when the load on the machine is heavy than when it is light.

4. The method of regulating a dynamoelectric machine, which consists in conducting current passing through the machine, through two parallel circuits, one of which includes a coil on the machine; and varying the current passing through the branch containin g the coil at a rate greater than the rate of variation of current in the other branch.

5. The method of compounding a directcurrent dynamo-electric machine, which consists in exciting the field of the machine by the combined action of two magnetomotive forces one of which is substantially constant, while the other has a rate of variation greater than the rate of change of load on the machine.

6. The method of exciting the field of a dynamo-electric machine, which consists in passing current through a field-coil on the machine, and controlling the flow of said current in such a manner that its rate of variation is greater than the rate of variation of load on the machine.

7. The method of shaping the external characteristic of a dynamo-electric machine, which consists in automatically compensating for the variation in voltage due to variation in permeability of the magnetic circuit.

In witness whereof I have hereunto set my hand this 22d day of August, 1898.

CHARLES 1. STEINMETZ.

\Vitnesses:

B. B. HULL, M. H. EMERSON. 

